Ink jet printhead

ABSTRACT

An ink jet printhead chip that is the product of an integrated circuit fabrication technique includes a wafer substrate having a front surface and a rear surface. A plurality of ink passages are defined through the wafer substrate, so that each ink passage defines an inlet at a rear surface of the wafer substrate and an outlet at a front surface of the wafer substrate. Each ink passage is in fluid communication with an ink supply at the rear surface of the wafer substrate. A plurality of actuators are positioned on the rear surface of the wafer substrate and are operatively arranged with respect to the ink passages to generate an ink flow through each passage, from the rear surface to the front surface, when activated.

REFERENCES TO US APPLICATIONS

This is a Continuation Application of U.S. Ser. No. 10/307,336 filedDec. 2, 2002, now allowed, which is a CIP of U.S. application Ser. No.09/112,778 filed on Jul. 10, 1998 now U.S. Pat. No. 6,416,168.

This application is a continuation application of U.S. Ser. No.09/900,159 filed Jul. 9, 2001, now U.S. Pat. No. 6,488,359, and U.S.Pat. Nos. 6,557,977, 6,227,652, 6,213,589, 6,247,795, 6,394,581,6,244,691, 6,257,704, 6,220,694, 6,234,610, 6,247,793, 6,264,306,6,241,342, 6,254,220, 6,302,528, 6,239,821, and 6,247,796 are herebyincorporated by reference.

FIELD OF THE INVENTION

This invention relates to ink jet printheads. More particularly, thisinvention relates to an ink jet printhead that incorporates through-chipink ejection nozzle arrangements.

BACKGROUND TO THE INVENTION

The Applicant has invented an ink jet printhead that is capable ofgenerating text and images at a resolution of up to 1600 dpi.

In order to achieve this, the Applicant has made extensive use of microelectro-mechanical systems technology. In particular, the Applicant hasdeveloped integrated circuit fabrication techniques suitable for themanufacture of such printheads. The Applicant has filed a large numberof patent applications in this field, many of which have now beenallowed.

The printheads developed by the Applicant can include up to 84000 nozzlearrangements. Each nozzle arrangement has at least one moving componentthat serves to eject ink from a nozzle chamber. The components usuallyeither act directly on the ink or act on a closure which serves topermit or inhibit the ejection of ink from the nozzle chamber.

The moving components within the printheads are microscopicallydimensioned. This is necessary, given the large number of nozzlearrangements per printhead. The Applicant has spent a substantial amountof time and effort developing configurations for such printheads.

One of the reasons for this is that, as is known in the field ofintegrated circuit fabrication, cost of on-chip real estate is extremelyhigh. Furthermore, it is important that levels of complexity are kept toa minimum since these significantly increase the cost of fabrication.

Integrated circuit fabrication techniques involve what is generally adeposition and etching process. As a result, devices which aremanufactured in accordance with such techniques are usually, ofnecessity, in a layered construction. Furthermore, it is important todevelop a configuration where a high number of devices can be fabricatedper unit area of chip surface.

The present invention has been conceived by the Applicant to address thedifficulties associated with achieving the high packing density of thenozzle arrangements and thereby to facilitate substantial cost saving inmanufacture.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided an inkjet printhead chip including:

-   -   a wafer substrate having a front surface and a substantially        planar rear surface, a plurality of ink passages being defined        through the wafer substrate, so that each ink passage defines an        inlet at the rear surface of the wafer substrate and an outlet        at the front surface of the wafer substrate, each ink passage        being in fluid communication with an ink supply at the rear        surface of the wafer substrate;    -   at least one closure member associated with each of the ink        passages, the at least one closure member being positioned on or        adjacent to the rear surface of the substrate and being        displaceable, in a plane parallel to the rear surface, between        open and closed positions to control a flow of ink through each        passage; and        at least one actuator associated with each closure member and        operatively engaged with the respective closure member to        displace the respective closure member between the open and        closed positions, when activated.

According to a another aspect of the invention, there is provided an inkjet printhead chip that is the product of an integrated circuitfabrication technique, the printhead chip comprising

-   -   a wafer substrate having a front surface and a rear surface, a        plurality of ink passages being defined through the wafer        substrate, so that each ink passage defines an inlet at a rear        surface of the wafer substrate and an outlet at a front surface        of the wafer substrate, each ink passage being in fluid        communication with an ink supply at the rear surface of the        wafer substrate; and    -   a plurality of actuators that are positioned on the rear surface        of the wafer substrate and are operatively arranged with respect        to the ink passages to generate an ink flow through each        passage, from the rear surface to the front surface, when        activated.

Preferably the roof walls, side walls and floor walls are positioned onthe rear surface of the wafer substrate to define a plurality of nozzlechambers, each roof wall defining an ink ejection port that is in fluidcommunication with a respective ink channel, an actuator beingoperatively arranged with respect to each nozzle chamber to eject inkfrom the nozzle chamber out of the ink ejection port and into the inkchannel.

Each actuator may include an ink displacement member that defines atleast the floor wall of each nozzle chamber, the ink displacement memberbeing movable towards and away from the roof wall of the nozzle chamberto eject ink from the ink ejection port.

Each actuator may include an actuating device that is positioned on therear side of the wafer substrate and is connected to the inkdisplacement member to move the ink displacement member towards and awayfrom the ink ejection port.

There may be a protective enclosure positioned on the rear surface ofthe wafer substrate, each actuating device being housed in theprotective enclosure.

Each actuating device maybe a thermal actuator, having a deformable bodyof expansion material that has a coefficient of thermal expansion whichis such that expansion of the material on the application of heat can beharnessed to perform work, the body being connected to an inkdisplacement member so that deformation of the body on the applicationof heat results in movement of the ink displacement member towards theink ejection port.

The protective enclosure may include a fluidic seal, the inkdisplacement member being connected to the deformable member through thefluidic seal.

According to a different aspect of the invention, there is provided anink jet printhead chip that is the product of an integrated circuitfabrication technique, the ink jet printhead chip comprising

-   -   a wafer substrate;    -   a plurality of ink passages defined through the wafer substrate,        so that each ink passage defines an inlet at a rear surface of        the wafer substrate and an outlet at a front surface of the        wafer substrate, each ink passage being in fluid communication        with an ink supply at the rear surface of the wafer substrate;    -   roof walls, side walls and floor walls that are positioned on        the rear surface of the wafer substrate to define a plurality of        nozzle chambers, each roof wall defining an ink ejection port        that is in fluid communication with a respective ink passage;        and    -   a plurality of actuators that are positioned on the rear surface        of the wafer substrate so that each actuator is operatively        arranged with respect to each nozzle chamber to eject ink from        the nozzle chamber and out of the ink ejection port.

The invention is now described, by way of examples, with reference tothe accompanying drawings. The specific nature of the followingdescription is not to be construed as limiting the scope of the abovesummary, in any way.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a three dimensional view of a first embodiment of part of aprinthead chip, in accordance with the invention;

FIG. 2 shows a sectioned side view of the printhead chip of FIG. 1;

FIG. 3 shows a sectioned side view of a second embodiment of a printheadchip, in accordance with the invention, with a nozzle arrangement of theprinthead chip in a pre-operative condition;

FIG. 4 shows the nozzle arrangement of FIG. 3, in a post-operativecondition;

FIG. 5 shows a side sectioned view of a third embodiment of a printheadchip, in accordance with the invention, with a nozzle arrangement of theprinthead in a pre-operative condition;

FIG. 6 shows a side sectioned view of the nozzle arrangement of FIG. 5,in a post-operative condition; and

FIG. 7 shows a sectioned side view of a fourth embodiment of a printheadchip, in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings, reference is made to a nozzle arrangement. It will beappreciated that the printhead chip of the invention comprises aplurality of the nozzle arrangements. Furthermore, as set out in thepreamble, the printhead chips can incorporate an extremely high numberof such nozzle arrangements. Accordingly, only one nozzle arrangement isshown in each of the drawings, for the sake of convenience and for easeof description. It will readily be appreciated that replicating each ofthe nozzle arrangements to a sufficiently high degree will provide areader with a configuration of the printhead chip, in accordance withthe invention.

In FIGS. 1 and 2, reference numeral 10 generally indicates a nozzlearrangement of a printhead chip, in accordance with the invention.

The nozzle arrangement 10 includes a substrate 12 forming part of theprinthead chip of the invention. The substrate 12 includes a wafersubstrate 14. An epitaxial layer 16 of boron doped silicon is depositedon a front surface of the wafer substrate 14. The epitaxial layer 16thus defines an etch stop layer 18. The wafer substrate 14 is etched todefine a nozzle chamber 20 so that the etch stop layer 18 defines a roofwall 22 of the nozzle chamber 20.

The roof wall 22 is itself etched to define an ink ejection port 23. Itfollows that the nozzle chamber 20 and the ink ejection port 23 togetherdefine an ink passage through the wafer substrate 14.

A drive circuitry layer 24 is positioned on a rear surface of the wafersubstrate 14 and incorporates drive circuitry (not shown) for the nozzlearrangement 10. An ink passivation layer 26 of silicon nitride isdeposited on the drive circuitry layer 24.

In this particular embodiment, a shutter member or shutter 28 ispositioned on the layer 26 and is displaceable between a closed positionin which the shutter 28 covers an inlet 30 of the nozzle chamber 20 andan open position in which ink is permitted to flow into the nozzlechamber 20. The shutter 28 has a toothed edge 32.

The nozzle arrangement 10 includes a micro electro-mechanical drivemechanism 34 to drive the shutter 28 between its closed and openpositions. In particular, the drive mechanism 34 includes a series ofgears 36, 38, 40 which engage the toothed edge 32 of the shutter 28. Inparticular, the gear 36 is driven by actuators 42. The gear 36 isengaged with the gear 38, which, in turn, is engaged with the gear 40.The gears 36, 38, 40 are configured to achieve a reduction effect on thegear 40. The gear 40 is engaged with the toothed edge 32.

The actuators 42 are electrically connected to the drive circuitry layer24 to be controlled via a suitable control system (not shown) which, inturn, is connected to the drive circuitry layer 24.

The drive mechanism 34, the ink passivation layer 26 and the shutter 28are all in fluid contact with an ink reservoir 44 (shown in FIGS. 3 to6).

In this embodiment, the ink within the ink reservoir 44 is repeatedlypressurized to an extent sufficient to facilitate the ejection of inkfrom the ink ejection port 23. Thus, by controlling operation of theshutter 28 via the drive circuitry layer 24 and the drive mechanism 34,selective ejection of ink from the ink ejection port 23 can be achieved.

It will be appreciated that, in this embodiment, the ink is ejectedthrough the wafer substrate 14 from the rear surface of the wafersubstrate 14 towards the front surface of the wafer substrate 14.

Details of the operation of the drive mechanism 34 and of the remainderof the nozzle arrangement 10 are set out in the above referenced USapplications. It follows that this detail will not be covered in thisspecification.

In FIGS. 3 and 4, reference numeral 50 generally indicates a nozzlearrangement of a second embodiment of a printhead chip, in accordancewith the invention. With reference to FIGS. 1 and 2, like referencenumerals refer to like parts, unless otherwise specified.

Instead of the shutter 28 used in combination with the repeatedlypressurized ink to achieve drop ejection, the nozzle arrangement 50includes an actuator 52 which acts directly on ink 54 in the nozzlechamber 20.

The actuator 52 includes a heater element 56 which is of a shape memoryalloy. In this particular example, the shape memory alloy is a nickeltitanium alloy.

Details of the shape memory alloy are provided in the above referencedUS applications and are therefore not set out in this specification.

The heater element 56 has a trained shape as shown in FIG. 4. A layer 58of silicon nitride is deposited, under tension, on the heater element56, with the heater element 56 in its martensitic phase. This causes theheater element 56, together with the layer 58, to bend away from the inkejection port 23, as shown in FIG. 3.

The heater element 56 is connected to the drive circuitry layer 24 withsuitable vias 60. Furthermore, the heater element 56 is configured to beresistively or joule heated when a current from the drive circuitrylayer 24 passes through the heater element 56. This heat is sufficientto raise the temperature of the heater element 56 above itstransformation temperature. This results in the heater element 56undergoing a crystalline change into its austenitic phase, therebyreverting to its trained shape as shown in FIG. 4. The resultantmovement results in the generation of a drop 62 of ink.

When the heater element 56 cools, the tension that has built up in thelayer 58 results in the heater element 56, now in its martensitic phase,returning to the position shown in FIG. 3. This facilitates necking andseparation of the drop 62.

In FIGS. 5 and 6, reference numeral 70 generally indicates a nozzlearrangement of a third embodiment of a printhead chip, in accordancewith the invention. With reference to FIGS. 1 to 4, like referencenumerals refer to like parts, unless otherwise specified.

The nozzle arrangement 70 includes an actuator 72 which also actsdirectly on the ink 54 within the nozzle chamber 20. However, in thiscase, the actuator 72 is hingedly connected to the substrate 12 to behingedly displaceable between the pre-operative position shown in FIG. 5and the post-operative position shown in FIG. 6.

The actuator 72 has a magnetic core 74 which is susceptible to amagnetic field of cyclically reversing polarity applied to the printheadchip. The cyclically reversing magnetic field tends to cause theactuator 72 to oscillate between the positions shown in FIGS. 5 and 6.The magnetic core 74 is sufficiently sensitive and the magnetic fieldsufficiently strong so that this oscillation, if unchecked, results inthe ejection of the drop 62 of the ink 54 from the ink ejection port 23.

The nozzle arrangement 70 includes a checking or obstruction mechanism78 which is positioned in a side wall 80 of the nozzle chamber 20. Theobstruction mechanism 78 is connected to the drive circuitry layer 24 tobe controlled with a suitable control system (not shown) also connectedto the drive circuitry. The obstruction mechanism 78 is configured sothat, when activated, an obstruction member 82 of the mechanism 78extends from the side wall 80 into the nozzle chamber 20. As can be seenin FIG. 5, this serves to obstruct movement of the actuator 72 into thenozzle chamber 20.

It will thus be appreciated that selective ejection of the ink 54 fromthe ink ejection port 23 can be achieved.

As with the previous embodiments, detail of the working and structure ofthe nozzle arrangement 70 is set out in the above referenced USapplications. The primary purpose of illustrating these examples is toindicate possible configurations which can be achieved when the ink isdisplaced from the rear surface of the wafer substrate 14 to the frontsurface, through the wafer substrate 14.

In FIG. 7, reference numeral 90 generally indicates a nozzle arrangementof a fourth embodiment of a printhead chip, in accordance with theinvention. With reference to FIGS. 1 to 6, like reference numerals referto like parts, unless otherwise specified.

In the nozzle arrangement 90, the wafer substrate 14 is etched to definean ink ejection channel 92. Furthermore, the nozzle chamber 20 isdefined by an ink ejection paddle 94 positioned behind the inkpassivation layer 26, side walls 96 extending from the ink passivationlayer 26 and a roof wall 98 spanning an inlet 100 to the ink ejectionchannel 92. Thus, the ink ejection paddle 94 defines a floor wall of thenozzle chamber 20. The roof wall 98 defines an ink ejection port 102. Itfollows that the ink ejection port 102 and the ink ejection channel 92together define an ink passage through the wafer substrate 14.

The ink ejection paddle 94 is shaped to define an included volume 104which forms part of the nozzle chamber 20. Furthermore, the ink ejectionpaddle 94 is partially received within the side walls 96. Thus, ondisplacement of the ink ejection paddle 94 towards the roof wall 98, avolume of the nozzle chamber 20 is reduced so that ink is ejected fromthe ink ejection port 102 to pass through the ink ejection channel 92and on to the print medium. The direction of movement of the inkejection paddle 94 is indicated by an arrow 106.

The ink ejection paddle 94 is connected to a thermal actuating device108. In order to protect the device 108, a silicon nitride enclosure 110is positioned on the passivation layer 26 to enclose the device 108.

The device 108 includes a deformable body 116 of expansion materialhaving a coefficient of thermal expansion which is such that, uponheating, expansion of the material can be harnessed to perform work. Thebody has a proximal planar surface 120, closest to the wafer substrate14, and an opposed distal planar surface 122. The device 108 includes aheater element 118 that is positioned in the body 116 to heat the body116. As can be seen in FIG. 7, the heater element 118 is positionedclosest to the distal surface 122. Thus, when the heater element 118 isactivated, the expansion material in a region proximate the distalsurface 122 expands to a greater extent than the remaining material.This results in the body 116 bending towards the substrate 14.

The body 116 is elongate, with one end attached to a support post 124 toprovide a bending anchor. An opposed end of the body 116 is free tomove. The heater element is connected to the drive circuitry layer 24with a suitable via 126 in the support post 124.

An arm 112 interconnects the body 116 with the ink ejection paddle 94.In order to achieve this, the arm 112 extends through a fluidic seal 114which is positioned in a wall 128 of the silicon nitride enclosure 110.

The enclosure 110, the ink ejection paddle 94 and the side walls 96 areall positioned in an ink reservoir, indicated at 130. The paddle 94 andthe side walls 96 are positioned so that ink is permitted to flow intothe nozzle chamber 20 from the ink reservoir 130, subsequent todisplacement of the paddle 94 away from the ink ejection port 102.

A particular advantage of this configuration is that the ink is ejectedfrom a point at the rear surface of the wafer substrate 14 to passthrough the wafer substrate 14. As a result, special preparation of thefront surface of the wafer substrate is not necessary. This simplifiesthe fabrication of the printhead chip with a resultant cost saving.

1. An ink jet printhead chip including: a wafer substrate having a frontsurface and a substantially planar rear surface, a plurality of inkpassages extending through the wafer substrate to define an inlet at therear surface of the wafer substrate and an outlet at the front surfaceof the wafer substrate, each ink passage being in fluid communicationwith an ink supply at the rear surface of the wafer substrate; at leastone closure member associated with each of the ink passages, the atleast one closure member being positioned on or adjacent to the rearsurface of the substrate and being displaceable, only in a planesubstantially parallel to the rear surface, between open and closedpositions to control a flow of ink through each passage; and at leastone actuator associated with each closure member and operatively engagedwith the respective closure member to displace the respective closuremember between the open and closed positions, when activated.
 2. The inkjet printhead of claim 1 wherein each closure member is constrained tomove between the open and closed position along a linear path.
 3. Theink jet printhead chip of claim 1 wherein each actuator engages therespective closure member via a gear train.
 4. The ink jet printhead ofclaim 3 wherein the gear train includes at least one rotating gear wheeland a linear gear.
 5. An ink jet printhead chip as claimed in claim 1,in which a drive circuitry layer is positioned on the rear surface ofthe wafer substrate and is electrically connected to the actuators, sothat the actuators can be activated by a signal received from the drivecircuitry layer.
 6. An ink jet printhead chip as claimed in claim 1, inwhich said each ink passage defines a nozzle chamber in the wafersubstrate.
 7. An ink jet printhead chip as claimed in claim 1, in whichthe wafer substrate defines a plurality of ink channels forming part ofrespective ink passages.